As light-emitting devices, application of organic EL devices to various apparatuses is being studied and put into practical use, and organic EL devices are being used, for example, as backlights for flat-panel displays and liquid crystal display apparatuses, or as light sources for lighting, and so on.
FIG. 6 is a cross-sectional view of a configuration of a typical organic EL device. As shown in FIG. 6, a typical organic EL device 100 is formed by stacking a reflective electrode 111, an organic layer 112, a transparent electrode 113, and a transparent substrate 114 in the stated order. The organic layer 112 is formed by stacking an electron injection layer, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and so on (not shown in the figure). It is typical to place the electron injection layer and the electron transport layer on the cathode-side, place the hole transport layer and the hole injection layer on the anode-side, and place the light-emitting layer in between the electron transport layer and the hole transport layer. Hereinafter, considering the case where the reflective electrode 111 is a cathode and the transparent electrode 113 is an anode, it is assumed that the electron transport layer and the hole transport layer are disposed to be in contact with the cathode and the anode, respectively. It should be noted that the same assumption can also be made in the case where the transparent electrode 113 is an anode and the reflective electrode 111 is a cathode.
In organic EL devices, there are many cases where the distance between a light-emitting position and the reflective electrode is set short (for example, 30 to 70 nm) in order to take advantage of the light interference effect to strengthen light in the frontal direction (upward direction in the figure). However, when the distance between the light-emitting position and the reflective electrode becomes short, the effects of surface plasmons are felt. Here, surface plasmons is an oscillation mode in which electrons in a surface of a metal oscillate collectively, and is a phenomenon that causes interaction between free electrons in the metal and light. In the organic EL device, metals such as aluminum (Al) and silver (Ag) are often used as the primary material for the reflective electrode, and, when the distance between the light-emitting position and the reflective electrode is short, part of the light generated at the light-emitting position is absorbed by the reflective electrode after bonding with surface plasmons. In such manner, in the organic EL device, there is the problem that light-emitting efficiency deteriorates due to the effects of surface plasmons.
In view of this, there is proposed a technique of improving light-emitting efficiency by exciting surface plasmons by providing, in the interface between the reflective electrode and the organic layer, protrusions having a regular pitch to thereby re-reflect light to the light-emitting layer side (Patent Literature (PTL) 1).